WISE colour–colour diagram. The variable AGN candidates included in the Gaia-CRF3 sample are marked in blue, while the CANOE objects are in red. Blazars are shown with larger (grey) symbols to highlight the ‘blazar strip’, which extends from the quasar locus to the early-type-galaxy region. Different types of stellar objects are also shown (see Gavras et al. 2023): constant stars (CST), eclipsing binaries (ECL), solar-like stars (with spots and flares), and ab-type RR Lyrae stars (RRab). Sources with G >  18 and H − K <  0.3 are discussed in the text.